The present invention concerns a device and a procedure for storing and dispensing chemical reagents. In particular, the invention concerns a device and a procedure for storing and dispensing biochemical reagents used in small volumes and therefore sensitive to contamination, oxidation and cross-reactions between the reagents.
Immunological methods such as RIA, EIA and ELISA have found widespread application in medical diagnostics during recent decades. (RIA, EIA and ELISA are abbreviations for Radioactive Immuno Assay, Enzyme Linked Immuno Assay and Enzyme Linked ImmunoSorbent Assay respectively). These methods quickly developed into standard procedures. To meet the demand for efficient handling with both manual and automated pipettes, as well as in detection instruments, standardised reaction vessels that could handle several samples at the same time were developed. These vessels are referred to as multi-sample plates in the remainder of this document.
A microtitre plate commonly consists of a rectangular plate formed from injection molded polystyrene plastic. The plate contains a number of hollows arranged in a grid. These hollows are known as wells and act as reaction vessels for individual chemical reactions. The three most important standards of microtitre plates are their outer dimensions that allow them to fit in standard instruments, their so-called grid spacing, which is the distance between the centre of one well to the centre of the adjacent well in the same row or column in the grid, and the position of the wells in relation to each other and to the outer edges of the plate. The most widely used microtitre plate format is approximately 128xc3x9785xc3x9714 millimeters with 96 wells arranged in a grid of eight rows and 12 columns. The grid spacing between wells is about nine millimeters. However, several other divisions are found within the above cited format. Usually encountered are also plates with 192, 384 or even more wells. Microtitre plates constituting one half of the above cited format are also in use. The most recent addition to this variety of multi-sample plates are the multi-sample plates used in so called multiple array technology, where extremely small volumes are ejected onto a surface, e.g. an absorbent surface. Examples of this technology include the multi-sample plates or sheets used in assays and procedures utilizing hybridization to High Density Oligonucleotide Arrays, e.g. detection of genetic mutations, genome screening or sequencing operations. Multi-sample plates used in the multi array technology are also referred to as nanotitre plates or nano-well plates. Also silicon chips or wafers, having areas for receiving reagents and samples, should be included under the definition xe2x80x9cmulti-sample platesxe2x80x9d.
Microtitre plates with wells arranged in a grid form are the most commonly used form of multi-sample plate. However, other arrangements of wells, such as circular forms, are also found in multi-sample plates.
When working routinely with microtitre plates, especially in areas of clinical application, the user aims to increase handling speed, i.e. the through-put speed of samples, by introducing various levels of automated system for the different steps. One such step is the handling of reagents.
Reagents can be handled with manually operated pipettes such as those known as plunger pipettes. For work with microtitre plates, multi-channel pipettes have been developed. These allow manual pipetting in complete rows or columns of wells in a single action. In aiming to further automate this pipetting work, a range of electronic instruments of varying complexity have also been developed. Examples include plunger pipettes with electronically driven step motors and multi-channel pipettes and dispensers with different types of pumps.
A high level of automation can be achieved by integrating units that position the reaction vessel in relation to the dispensing mouthpiece and units for the computerised control of this positioning in relation to the pipetting process. An instrument with such a high level of automation is usually called a pipetting robot. In other words, a pipetting robot comprises three main functional units. Firstly, a dispensing unit that comprises one or more individual precision pumps. The function of this type of precision pump is to dispense a specified volume of liquid through the mouthpiece at a specific time. Secondly, a pipetting robot comprises a positioning unit that orientates the position of the dispensing mouthpiece in relation to the reaction vessel at the exact moment of dispensing. Thirdly, an electronic control unit.
The difficulty in constructing a pipetting robot of the kind described in the previous paragraph is to achieve a sufficiently high level of precision regarding a number of key functions. One key function of a pipetting robot is the accuracy of the average amount of liquid dispensed and the standard deviation between different pipetting actions In general, the degree of accuracy is less when pipetting small volumes than when pipetting large volumes. A further key function is naturally the speed of operation measured as the number of completely dispensed samples per unit of time. It has proven difficult to construct robots that are both accurate when dispensing small volumes and sufficiently quick to meet the demands of molecular biological work in a clinical environment, for example.
In addition to these main functional characteristics of a pipetting robot, there are other characteristics that can also be important. Examples of such characteristics are purchase price, cost effectiveness for small series of samples, instrument size, and the requirement for cleaning the mouthpiece and other parts to help prevent contamination by foreign material and material from previous pipetting actions. In addition, the reaction vessel, the sample and the chemicals should be protected from exposure to air-borne particles that can carry such contaminating material.
Today, there are pipetting robots that differ with regard to whether they have separate mouthpieces for suction and dispensing or whether the same mouthpiece is used for both functions. The first type incorporates one or more suction mouthpieces connected with one or more liquid reservoirs, i.e. vessels from which the reagents shall be dispensed. These reagents pass from this vessel through the suction mouthpiece and via the dispenser unit to one or more dispensing mouthpieces from where they are transferred to the reaction vessel. This type of pipetting robot is subsequently referred to as a pump dispenser.
The second type of pipetting robot features one or more combined suction and dispensing mouthpieces. This type has a stand-alone liquid reservoir. The chemical reagents are drawn up from the sample vessel to the mouthpiece and are then dispensed into the reaction vessel with the same mouthpiece. This type of pipetting robot is subsequently referred to as a pipette dispenser.
The pump dispenser type of pipetting robot meets normal demands for accuracy, even when dispensing small volumes. It does not, however, fulfil the demands for speed of operation. In contrast, the pipette dispenser type of pipetting robot does meet normal demands for speed of operation. However, it does not normally meet the demands for a high degree of accuracy, which is one of the main pre-requisites.
A further problem is that neither type of pipetting robot is cost effective for small series of samples, i.e. handling about 500 samples or less. Protection against air-borne contamination can also be a problem. In addition, pump dispensers are very expensive to purchase and it is often difficult to clean their mouthpieces.
Those operations relevant to this invention that are today performed with conventional techniques, either manual or automatic, are, in chronological order the industrial synthesis of reagents, their storage in large packs, transport of these packs to the user, measuring out the relevant reagent volumes and dispensing these volumes in the appropriate sample wells or reagent vessels, such as the multi-sample plate, for example. When the actual sample has been applied and mixed with the reagents in the wells or equivalent intended for use in the multi-sample plate, this vessel is fully prepared and placed in an instrument or other location for incubation.
Pipetting robots are mainly used for two operations in this chain of events. They are used partly in connection with the industrial synthesis of reagents and their storage in large packs. These robots are frequently the pump dispensing type and are often large, expensive and relatively slow. They are, however, very accurate and form part of a quality-assured process with regard to all possible contamination threats, risks of mix-up, and similar hazards. Pipetting robots are also employed in the user""s laboratory for measuring out relevant reagent volumes and dispensing these in, for example, a multi-sample plate where a certain analysis is to be performed. These pipetting robots can be of different types but they must be quick and cannot be bulky or expensive. For these reasons they are usually not as accurate as the former type mentioned. One problem in the user""s laboratory can be the risk of contamination due to particles normally carried in the air, aerosols, splashing or via the mouthpiece or other component. The risk of mixing up bulk packs, for example, is especially great when many short series of samples are run or many different users are involved. In this context, sample means a patient sample, test material or other ingredient chosen by the user, of which the sample forms a part of the reagent mixture that is to be prepared.
It would be extremely advantageous if one could combine the advantages of the pipetting robot used in industrial context, i.e. accuracy and security with regards to contamination, mix-up and similar risks, with the advantages of the pipetting robot employed in the user""s laboratory, i.e. speed, low price and compactness.
This could be achieved by replacing the storage of industrially synthesised reagents in bulk packs with storing the reagents directly in the end user""s reaction vessel, which is then transported to the user""s laboratory with the ready mixed reagents. Only ample application then takes place in the laboratory. This ensures rapid, accurate and secure handling in this environment. The need for a pipetting robot is thus eliminated and the advantages of low price and compact size can thus be considered to have been fulfilled.
This solution is nevertheless associated with two disadvantages. Firstly, different end users prefer different types and manufacturers of reaction vessels, which makes efficient industrial handing difficult. Secondly, pre-mixing the reagents in the reaction vessel can start various chemical processes that reduce sensitivity and shelf life, which can in turn lead to incorrect sample results.
U.S. Pat. No. 3 554 705 describes a chemical package or crude reagent cartridge containing different reagents in separate storage chambers adapted for communication with, said compartments being closed with restraining means preventing the premature movement of the prepacked reagents from each of said storage chambers. This construction resembles the blister packaging system, used for solid and particulate matter. Although no volumes are mentioned in the description and claims, the construction of the storage chambers makes it clear, that they are intended to contain volumes in the order of magnitude of milliliters and in no case volumes so small, that they resist gravity and require centrifugation to leave the cartridge.
EP 678 745 A1 represents a more recent approach where a sample is transferred through centrifugation from a pointed vessel to a reaction vessel, where the latter is covered by a membrane and the pointed vessel penetrates said membrane. This system does not, however, concern the storage and dispensing of reagents and lacks the benefits, associated with the present invention.
A number of special problems arise when using the extremely small volumes that are typical in this context, i.e. in the order of a few xcexcl and less. For example, the volumes are so small that a force is required to detach them from the sides of the vessel or container in which they are stored. These volumes are often protected from evaporation and oxidation by a layer of wax or viscous oil. In practice, a force greater than gravity is needed to transfer the reagent from the dispensing container or device to the reaction vessel.
The aim of the present invention is to provide a device that conforms with current standards and working methods, especially those applied in biochemical analysis. Biochemical analysis refers to procedures to detect biochemical components, e.g. proteins, enzymes, and oligonucleotides, or for detecting the presence of specific cells, e.g. disease-causing organisms or cells that have undergone a pathogenic transformation, such as cancer cells. In particular, the aim of the invention is to provide a system that permits the safe and contamination-free storage of reagents, accurate dispensing with a high level of reproducibility, and simple handling that minimises the number of user operational steps. One aim is to eliminate the need for manual or automated pipetting by the user, i.e. in the laboratory where the analysis is performed.
The drawbacks of current techniques described above are overcome by the present invention as described in the attached claims. In particular, the invention concerns a device and a procedure for storing and dispensing biochemical reagents used in small volumes and therefore sensitive to contamination, oxidation and cross-reactions between the reagents.